EDR/DTW Only stretch one signal

I am working with ultrasound signals that are affected by a temperature change, I would like to use EDR/DTW (or whatever is most appropriate) to re-align the temperature shifted signal with a baseline signal, so that I can use subtraction methods to compared changes in amplitude between the two signals.

The problem with EDR/DTW is that both signals are stretched, I would like to only stretch the second signal (120°C), so that when I apply this transform to other signals the baseline signal (20°C) is always unaffected.

You can see the stretching of both signals in the following example code (data attached):

M1 = readmatrix("example_data.csv");
A1 = M1(8:end,:);

Time = A1(:,1);
S0_20C = A1(:,2);
S0_120C = A1(:,3);

[dist,ix,iy] =edr(S0_20C,S0_120C,0.001);

hold on
grid on
plot(S0_20C)
plot(1:numel(ix),S0_20C(ix),'.-', ...
     1:numel(iy),S0_120C(iy),'.-');
legend('Original 20C', 'EDR 20C','EDR 120C')

Any suggestions are appreciated.

Answer 1

[Prathamesh]

Hi @Lawrence Yule,

I understand that the you are working with ultrasonic sounds and would like to use ‘EDR/DTW’ to re-align the temperature shifted signal with a baseline signal. But the problem with ‘EDR/DTW’ is that both signals are stretched, but you want to only stretch the second signal (120°C), so that when you apply this transform to other signals the baseline signal (20°C) is always unaffected.

To align your 120°C signal to the 20°C baseline without altering the 20°C data, follow these steps:

• Calculate the warping path between the two signals using the ‘dtw’ function.

[~, path_20C, path_120C] = dtw(S0_20C, S0_120C);

• Create the warped 120°C signal by interpolating the original 120°C data onto the 20°C timeline.

warped_S0_120C = interp1(Time(path_20C), S0_120C(path_120C), Time, 'linear');

• You can now use ‘S0_20C’ (your fixed baseline) and ‘warped_S0_120C’ for plotting and subtraction.

Refer below documentation link :

‘dtw’ : https://www.mathworks.com/help/signal/ref/dtw.html

‘interp1’: https://www.mathworks.com/help/matlab/ref/double.interp1.html